1. Field of the Invention
The present invention generally relates to a hole saw guide apparatus for guiding hole boring tools and more particularly pertains to a hole saw guide which may be utilized for enlarging existing holes in a workpiece.
2. Description of the Prior Art
The use of a hole saw guide is known in the prior art. More specifically, hole saw guides heretofore devised and utilized for the purpose of enlarging existing holes are known to consist basically of familiar, expected and obvious structural configurations, notwithstanding the myriad of designs encompassed by the crowded prior art which have been developed for the fulfillment of countless objectives and requirements.
For example, U.S. Pat. No. 4,579,486 to Damico discloses a Hole Saw Guide used to position a hole saw while forming a new hole of larger diameter with or without maintaining concentricity with the existing hole. The Damico invention permits enlargement of an existing hole by employing a plurality of screws and locking nuts or sliding arms to engage the existing hole sidewalls and thereby locating a guide hole for the pilot drill of a larger hole saw. The Damico invention means for assuring concentricity of the enlarged hole with respect to the existing hole comprises adjustable arms or screws which engage the sidewalls of the existing hole. Since there is no provision for maintaining an isometric relationship of the independently adjustable arms or screws there cannot be an assurance of concentricity without difficult and tedious readjustment and mensuration. The present invention has the advantage of assured concentricity by maintaining the axis of the pilot drill hole on the existing hole axis.
In U.S. Pat. Nos. 5,074,722 to Cochran, 4,596,499 to Fangmann, and 5,069,584 to Obermeier various forms of rotary cutting and drilling tools are disclosed. A disadvantage in this prior art is the lack of a means for employing a common hole saw for enlarging a previously bored hole in the workpiece. The present invention employs an inexpensive common hole saw to perform hole enlargement.
In U.S. Pat. No. 3,630,632 to Holleman a centering attachment for a cylinder boring device is described. This prior art, although devised for cylinder boring, has application to enlarging deep existing holes by employing a boring bar with centering means and does not have the advantage of application to the more commonly used hole saw. A disadvantage resulting from the centering means disclosed in this prior art renders its use unsuitable for reforming shallow holes of uniform resulting diameter unless a short concentric cylinder is applied. Application of the short concentric cylinder is generally unfeasible without the addition of costly apparatus. The present invention enables enlarging existing holes without application of an external cylinder or excessive cost.
As illustrated by the background art, efforts are continuously being made to attempt to form and enlarge holes. No prior effort, however, provides the benefits attendant with the present invention. Additionally, the prior patents and commercial techniques do not suggest the present inventive combination of component elements arranged and configured as disclosed and claimed herein.
Therefore, it can be appreciated that there exists a continuing need for a hole saw guide which can be employed to provide a means for enlarging existing holes. In this regard, the present invention substantially fulfills this need.
The present invention achieves its intended purposes, objects, and advantages through a new, useful and unobvious combination of method steps and component elements, with the use of a minimum number of functioning parts, at a reasonable cost to manufacture, and by employing only readily available materials.